1. Field of the Invention
The present invention relates to an apparatus for winding a multi-layer coil in a trapezoidal winding space, and a method of winding such a coil.
2. Description of Related Art
A conventional apparatus for winding a multi-layer coil in a winding space having a trapezoidal cross-section is shown in FIGS. 11A-11D. A bobbin 100 is composed of a center pillar 102, a small flange 104 connected to one end of the center pillar 102, and a large flange 106 connected to the other end of the center pillar 102. A wire 200 is wound in a winding space formed outside of the center pillar 102 between the small flange 104 and the large flange 106. The winding space has a trapezoidal cross-section in a plane cut through a center axis of the center pillar 102.
The wire 200 is wound in the winding space in a winding process shown in FIG. 11A through FIG. 1D. The bobbin 100 is fixed to a rotating shaft such as a rotating spindle (not shown), and a wire 200 is fed from a feeder nozzle 36. The feeder nozzle 36 is connected to a holder 34 that is supported on a shaft 32 and is movable back and forth in a direction along the center axis of the bobbin 100. As shown in FIG. 11A, the wire 200 is wound in a space between the large flange 106 and the small flange 104 until layers of the wire reach a height of the small flange 104. Thereafter, as shown in FIGS. 11B-11D, the number of wire-turns in one layer is gradually decreased until a top layer reaches the height of the large flange 106. In this particular example shown here, two turns, i.e., two-wire-pitches, are decreased layer by layer. According to the movement of the feeder nozzle 36 in the axial direction, the winding direction of each layer is switched at a turning position at the right side. In this manner, a coil 110 is wound in the trapezoidal winding space.
Since the wire 200 is simply guided by the feeder nozzle 36 in the conventional winding process, the turning position of each layer may be deviated from an intended turning position. This means that the coil 110 may be wound in an irregular shape, resulting in decrease in a space factor of the coil 110 in the winding space. The space factor is defined as a ratio of a total cross-sectional area of the wire 200 relative to a cross-sectional area of the winding space. In addition, the wire 200 crosses over the wire of a lower layer at the turning position, and an outer diameter of the coil 110 is enlarged at the cross-over points. Therefore, if the turning positions deviate in the circular direction, the diameter of the coil 110 becomes large. This also results in a decrease in the space factor.
It would be possible to suppress the deviation of the turning positions by decreasing a winding speed or by temporarily stopping the winding process at each turning position. However, this reduces the winding speed and sacrifices production efficiency.